Method of making a single-crystal turbine blade

ABSTRACT

A single-crystal turbine blade and a method of making such single-crystal turbine blade are disclosed. During manufacturing, a secondary crystallographic orientation of the material of the single-crystal turbine blade is controlled based on a parameter of a root fillet between an airfoil of the single-crystal turbine blade and a platform of the single-crystal turbine blade. The parameter can be a location of peak stress in the root fillet expected during use of the turbine blade.

TECHNICAL FIELD

The disclosure relates generally to gas turbine engines, and moreparticularly to manufacturing turbine blades.

BACKGROUND

Turbine blades for gas turbine engines may be manufactured usingnickel-based superalloys or other metal systems. Mounted on turbinediscs, these blades may spin at high speeds in gas streams of 1500° C.or higher. The design of turbine blades involves selecting anaerodynamically effective shape to achieve gas turbine performanceobjectives. The design also involves selecting turbine blade material toensure turbine blades can have the requisite strength and durability.During gas turbine operation, some regions of the turbine blade canexperience high steady-state stress and vibratory stress correspondingto low order dynamic modes for example. Existing methods of designingand manufacturing turbine blades may lead to increasing weight and/orcompromising aerodynamic performance in order to meet strength anddurability requirements.

SUMMARY

In one aspect, the disclosure describes a method of making asingle-crystal turbine blade with a material having a face centeredcubic crystallographic structure. The method comprises: duringmanufacturing of the single-crystal turbine blade, controlling asecondary crystallographic orientation of the material based on aparameter of a root fillet between an airfoil of the single-crystalturbine blade and a platform of the single-crystal turbine blade.

In another aspect, the disclosure describes a turbine blade comprising:

an airfoil made of a material having a single-crystal face centeredcubic crystallographic structure;

a platform connected to the airfoil; and

a root fillet defined between the airfoil and the platform;

wherein a secondary crystallographic orientation of the material isbased on a parameter of the root fillet.

In a further aspect, the disclosure describes a method of making aturbine blade including an airfoil made of a material having asingle-crystal crystallographic structure, a platform connected to theairfoil and a root fillet defined between the airfoil and the platform.The method comprises:

determining a location of peak stress in the root fillet expected duringuse of the turbine blade; and

during manufacturing of the turbine blade, controlling a secondarycrystallographic orientation of the material based on the location ofpeak stress in the root fillet.

Further details of these and other aspects of the subject matter of thisapplication will be apparent from the detailed description includedbelow and the drawings.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a turbofan gas turbineengine having one or more turbine blades as described herein;

FIG. 2 shows an embodiment of a turbine disc of a gas turbine enginewith mountable turbine blades;

FIG. 3 shows an embodiment of a turbine blade suited for mounting in aturbine disc of a gas turbine engine;

FIG. 4 shows a root fillet formed between an airfoil and a platform of aturbine blade;

FIG. 5. shows conventional Miller indices for a cubic crystallographicsystem;

FIG. 6 shows an exemplary single-crystal turbine blade manufacturedaccording to some aspects of the present disclosure;

FIG. 7 shows a stress distribution in a root fillet of a single-crystalturbine blade made of a material where a primary crystal axis iscontrolled and a secondary crystal axis is uncontrolled;

FIG. 8 shows a schematic of an embodiment of a single-crystal turbineblade manufactured according to some aspects of the present disclosure;and

FIG. 9 shows stress distribution in a root fillet of a single-crystalturbine blade manufactured according to some aspects of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure relates to single-crystal turbine blades andmethods of manufacturing thereof. In some embodiments, the methodsdisclosed herein can help reduce one or more peak stress valuesparticularly in the root fillet region, i.e. the fillet formed betweenthe turbine blade airfoil and platform, compared to existingsingle-crystal turbine blades.

The concepts disclosed herein are broadly applicable to turbine bladesconstructed of any suitable materials, however, these concepts areparticularly useful when applied to metallic materials intended for useat elevated temperatures. Typical of such metals are the nickel andcobalt based superalloys which possess relatively high strength andoxidation and corrosion resistance under demanding conditionsencountered in gas turbine engines.

In the discussion which follows, reference is made to single crystals.This term is intended to mean crystalline materials free from high anglegrain boundaries. The term “single crystal” is intended to encompassmaterials which contain non-mobile low angle grain boundaries anddislocation arrays. Also covered by this term, as used herein, arematerials having a regular crystalline matrix which contains a dispersedsecond phase which may be coherent or non-coherent with the matrixphase. Examples of such materials are nickel based superalloys whichcontain a coherent dispersion of gamma prime particles in a gammamatrix, and eutectic materials.

Aspects of various embodiments are described in relation to the figures.

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. The turbine section maycomprise one or more turbine(s) 20 arranged along a central axis c-c ofthe gas turbine engine 10. In some embodiments, engine 10 may be aturbo-fan engine. However, it is understood that aspects of the presentdisclosure are applicable to other types of engines such as turbo-propand turbo-shaft for example. A turbine 20 may comprise turbine disc 35(shown in FIG. 2) having attached thereto a plurality of turbine blades29 (shown in FIG. 2).

FIG. 2 shows an embodiment of a turbine disc 35 of a gas turbine enginewith mountable turbine blades 29. The turbine blades 29 may beconfigured to be removably attached to the turbine disc 35. The turbinedisc 35 may comprise a central axis c-c aligned (e.g., coaxial) with thecentral axis of the gas turbine engine 10.

FIG. 3 shows an embodiment of the turbine blade 29 suitable for mountingto the turbine disc 35 of a gas turbine engine 10 and may comprise ablade airfoil 30 and a blade platform 31. In some embodiments, a rootportion 37 of the blade platform 31 may be configured to be receivedinto a complementary slot 22 (shown in FIG. 2) formed in the turbinedisc 35. In some embodiments, the root portion 37 and the slot 22 in theturbine disc 35 may form a dovetail joint. In some embodiments, theturbine disc 35 and blades 29 may be part of an integral whole (e.g.,have a unitary construction, be integrally formed). In such anembodiment, a portion of the turbine disc 35 may define the bladeplatform 31.

Hot combustion gases exiting the combustor 16 of the gas turbine engine10 may enter the turbine section 18 of the gas turbine engine 10 and,after possibly flowing through one or more stator sections, may impingeon the blade airfoils 30 to generate forces on the turbine blades 29.The turbine disc 35 may define a coordinate system wherein a first axis(y) is parallel to the centerline c-c of the engine 10 about which thedisc 35 rotates, a second axis (z) coincides with a radial direction ofthe engine 10, and a third axis (x) is mutually perpendicular to the zand y axes. The airfoil stacking line 40 is a reference line commonlyused to designate the position in space of planar cross sections of theturbine blade 29 and may lie along the aforementioned z axis. Theairfoil stacking line 40 may extend radially from centerline c-c.

The platform 31 may be connected to a root portion 37 for mounting tothe disk 35 to transfer torque to the turbine disc 35, about the centralaxis c-c of the turbine disc 35, upon receiving a gas impingement. Theairfoil 30 may have a non-convex (e.g., concave) side, also called thepressure side 32, and a convex side, also called the suction side 34.The platform 31 may be disposed and connected to the base of the airfoil30. The platform 31 may extend generally transversely to the bottom ofthe airfoil 30.

In use, the turbine blade 29 may become heated as the airfoil 30 issubjected to impingement of hot combustion gases while mounted to theturbine disc 35, spinning at high speeds in a gas stream of 1500° C. orhigher. In addition, there may be varying mechanical loads, both steadyand vibratory, due to the spinning of the disc-mounted blade 29 aboutthe central axis c-c of the engine 10. The combined mechanical andthermal loadings are such that the turbine blade 29 may be prone to highstresses in certain regions of the blade 39. One such region is the rootfillet 38 formed at the intersection of the blade airfoil 30 and theblade platform 31. During engine operation, the root fillet 38 may beespecially prone to experience high steady-state stress and also highvibratory stress corresponding to varying dynamic modes of the gasturbine engine 10 for example.

FIG. 4 shows a root fillet 38 of an embodiment of the turbine blade 29.The root fillet 38 may comprise an edge 44 proximal to the bladeplatform 31 and an edge 42 proximal to the blade airfoil 30. The edges42, 44 may be fillet runout curves. The curved surface 45 between thetwo edges 42, 44 may experience relatively high amplitude (e.g., slowlyevolving) stresses.

Turbine blades 29, or part(s) thereof (e.g., airfoil 30 and/or rootfillet 38) may be manufactured from a material with a crystal structuredesigned to withstand the high mechanical and thermal loads, e.g. nickelbased superalloys. It may be advantageous to control the orientation ofthe crystal structure of the material of the blade 29 to obtain desiredproperties, and particularly lower stresses in the root fillet 38.

FIG. 5. shows the conventional Miller indices 46 for an octal unit cell58 of a cubic crystallographic system such as body centred cubic (BCC)or a face centred cubic (FCC) crystal, characteristic of some metals ormetal systems such as superalloys comprising nickel, aluminum, copper,and/or chromium. A crystal of one of these materials may have anorientation which can be defined using such Miller indices 46. In thecubic system of FCC and BCC crystals, specification of the orientationin space of any two orthogonal axes may fully define the orientation ofa crystal, e.g. fixing the [100] axis fixes the remaining crystal axesto an orthogonal pair lying in a plane perpendicular to the [100] axis,then further fixing the [001] axis fixes the orientation in this plane,thereby fully specifying the crystal orientation. Because of symmetry,various other directions in a crystal may be equivalent. Thus, ourdiscussion herein regarding any particular indices [PGR] will beinstructive for a full set of equivalent directions <PGR>.

Properties (e.g., mechanical properties, Young's modulus) of acrystalline material may vary with orientation of the crystallinestructure and thus it may be advantageous to control crystal orientationduring manufacturing of the turbine blade 29. Referring to FIG. 5,material properties along the [010] may be the same as the propertiesalong the [001] axis. Lying in the plane of the [100] and [010] axes isthe 110 axis at a 45° angle to the [100] axis. The properties of thecrystal material along [110] may be vary from the properties along [100]and [010]. As a matter of convention, the axes [100], [110] and [010]are characterized as “secondary axes”', and their orientation withrespect to the axes (x, y, and z) of a part (i.e., orientation ofcrystal axes within x-y planes transverse to the z axis) is called the“secondary crystallographic orientation” or simply “secondaryorientation”. However, it should be evident inasmuch as the axes arefixed by the crystal structure, reference to any other axis as secondarywould be equally definitive.

Directional solidification is a method of casting involving the use ofcontrolled cooling to cause a solidification interface to moveprogressively through a mold filled with molten metal. In someembodiments of this method, a low-temperature “chill plate” is placed atthe bottom of a ceramic mold containing the metallic melt. The meltclosest to the chill plate solidifies first due to the lower temperatureand establishes a solidification front in the melt, the front moving ina direction away from the chill plate. The nature of nickel-based alloysolidification is such that the [001] axis direction of the crystalsinherently lie along the direction of the solidification, unless seedingor other techniques are used. In situations where a set of separatecolumnar grains with aligned [001] axes is produced, the columnar grains26 may produce desirable properties in the part in the direction alongwhich the columnar grains lie. In the planes perpendicular to the lengthof the columnar grains the secondary crystallographic orientations mayvary at random. Thus, the material will have two different sets ofmechanical properties; a first set of longitudinal mechanicalproperties, and a second set of transverse mechanical properties. Thematerial is said to be transversely isotropic.

The directional solidification process a single-crystal metallic partswith one controlled axes as described by Piearcey in U.S. Pat. No.3,494,709 for example. In a solidification of FCC metallic alloys, suchas superalloys used in gas turbine engines, a part such as the turbineblade 29 solidified accordingly can have a controlled primarycrystallographic orientation [001] and a randomly-oriented secondarycrystallographic orientation [100]. The primary crystallographicorientation may be the crystallographic orientation which lies along theaxis along which the solidification interface moves and, for the turbineblade 29, may be chosen to be the airfoil stacking line 40 or othersuitably chosen axis.

A resulting single-crystal turbine blade 29 may have desirable materialproperties in the primary crystallographic orientation, e.g. crackingand subsequent propagation between blade airfoil 30 leading and trailingedges may be reduced by controlling the primary crystallographicorientation during manufacturing to be aligned with an airfoil stackingline 40 or other direction traverse to an axis connecting the leadingand trailing edges of the airfoil 30. The properties of a part willdepend on how the axes of the single crystal are oriented with respectto the part axes. Cast superalloys are metals that may be suitable forhigh temperature (˜650° C.) service. Single-crystal turbine blades maybe made from various superalloys, including those derived from nickelsuperalloy materials and other alloys used in the past in equiaxed andcolumnar grain castings. Aspects of the present disclosure are relevantto nickel based alloys and also other FCC materials such as alloys ofcobalt, iron and other metals and metal systems.

Directional solidification processes as taught by Piearcey or otherprocesses to produce single-crystal parts may be suitable for makingsingle-crystal articles in aspects of the present disclosure. Asingle-crystal part manufactured in such a manner may exhibit three-foldorthotropy, i.e. the orthotropy produced by fixing, duringmanufacturing, all the crystal axes to produce the single crystal. Asmentioned previously, all three axes of a single-crystal structure canbe fixed by fixing both a primary and secondary crystallographicorientation of the crystal. Turbine blades 29 may manufactured as singlecrystals. The secondary orientation of the crystal may also becontrolled using suitable manufacturing processes.

In some embodiments using directional solidification, a single crystalwith controlled primary and secondary crystallographic orientations maybe obtained by using seeding. In seeding, a previously made singlecrystal may be placed at the bottom of the mold in contact with the meltat one end. When molten metal contacts the seed, it may partially meltthe seed. When the melt is progressively cooled, the crystal growth isepitaxial from the seed. In some embodiments of “high rate” directionalsolidification, a seed is placed on a chill plate at the bottom of aceramic mold. Seeding has been used in instances both where orientationis to be controlled, and where it is simply a convenient technique forforming a single crystal. When a single-crystal structure is initiatedin molten metal, it is caused to propagate through the molten casting byprogressively moving a thermal gradient through a part. Often, thecrystal growth must take place transverse to the direction in which theprimary thermal gradient is moved. This is the situation, for example,when the part has a body with an overhanging flange. The crystal mustgrow laterally while the gradient continues to move along the primaryaxis of the part. In other embodiments, a different approach may be usedto manufacture single-crystal parts: single-crystal pieces may be formedseparately and then diffusion bonded together, to form a unitary part.However, this is only accomplished when the respective parts havematching crystallographic orientations. In still other embodiments, twoor more seeds are provided with a mold containing molten metal.Directional solidification is then carried out so that separatesolidification interfaces move simultaneously through the molten metal,emanate from each seed, and the interfaces merge thereafter into aunitary solidification interface. The unitary interface is then causedto move through the molten metal in the mold, to form the article.

A single-crystal article made in conformance with the foregoing methodwill be one which substantially has properties associated with an idealsingle-crystal article with a possible mismatch in orientation where theseparate solidification interfaces merge. So long as the mismatch isless than a critical value at which mechanical properties may sharplydecrease, the article and the method of making it may be considered tobe a method for manufacturing a single-crystal article with a controlledprimary and secondary orientations, i.e. all three axes aresubstantially controlled during manufacturing.

The aforementioned manufacturing methods and others that producesingle-crystal articles having a substantially controlledcrystallographic orientation are intended to be within the scope ofmanufacturing processes for single-crystal articles, with controlledprimary and secondary crystallographic orientations, envisaged in theaspects of the present disclosure. For example, in some of suchmanufacturing methods the orientation of the different axes may becontrolled to within 5° but not necessarily exactly.

FIG. 6 shows an exemplary single-crystal turbine blade 29 manufacturedaccording to some aspects of the present disclosure. Crystal axes 66 anda reference plane 64 are shown. In order to reduce stresses in the rootfillet 38 of the turbine blade 29, e.g. the previously mentionedstresses arising due to slowly-varying dynamic modes, aspects of thepresent disclosure may involve substantially controlling, duringmanufacturing using a single-crystal manufacturing method that allowssubstantial control of the complete crystal orientation, both theprimary and secondary crystallographic orientations of the crystalstructure in accordance with one or more parameters (e.g., geometry,edge, location of peak stress and/or other properties) of the rootfillet 38. In some embodiments, the crystallographic orientations may becontrolled, at least substantially, using one of the manufacturingprocesses mentioned above.

In some embodiments, the secondary crystallographic orientation [100]may be substantially controlled so that it is approximately parallel(e.g., tangent) to a portion of an edge 42, 44 of the root fillet 38.The edge may be the edge 42 proximal to the blade airfoil 30. In someembodiments, the portion of the edge 42 may be proximal to or on thesuction side 34 of the blade airfoil 30. A secondary crystallographicorientation

may then be controlled to be orthogonal to the primary crystallographicorientation [001].

In some embodiments, a reference plane 64 may be defined as normal tothe portion of the edge 42 of the root fillet 38 and passing through anominal point 56 in a target portion 54 of the root fillet 38. Theprimary crystallographic orientation [001] may lie in the referenceplane 64.

In various embodiments, the nominal point 56 may be a location ofexpected highest, or peak, stress in the root fillet 38 during use ormay be a location where stress reduction is important for improving rootfillet durability, or any other location important for turbine bladestructural integrity during gas turbine operation. Such location(s) maybe determined by experimental testing, performing calculations usingknown relationships relating to stresses in turbine blades, analyzinghistorical data from in-service turbine blades or turbine bladesotherwise carried into operation, or performing simulations andcalculations involving finite element analyses of a turbine blade underloading, or any other method for determining locations important forturbine blade structural integrity.

FIG. 7 shows a stress distribution in a root fillet 38 of asingle-crystal turbine blade made of a material wherein a primarycrystallographic orientation is controlled and the secondarycrystallographic orientation is left uncontrolled. The stressdistribution may be calculated using finite element analysis. Thecalculated stress distributions shows a location of peak stress 68 inthe root fillet. Such a location may be chosen as the nominal point 56in some embodiments of aspects of the present disclosure for the purposeof controlling the secondary crystallographic orientation. The stressdistribution also shows a root fillet stress being a peak stress in alower portion of the turbine blade 29.

FIG. 8 shows a schematic of an embodiment of a single-crystal turbineblade 29 manufactured according to some aspects of the presentdisclosure, the schematic showing crystal axes 66, a reference plane 64,and a reference conical surface 70. In such and other embodiments, thesecondary crystallographic orientation [100] may be substantiallycontrolled so as to be oriented approximately parallel to a portion ofan edge 42 (e.g., a fillet runout curve) (see FIG. 4) of the root fillet38 and passing through the nominal point 56. For example, the nominalpoint 56 may be chosen using one of the methods described previously.The reference plane 64 may further be defined as passing through thenominal point 56 and being normal to the portion of the edge 42 of theroot fillet 38 used to define the secondary crystallographic orientation[100]. A reference conical surface 70 may also be defined with respectto the nominal point 56 and the parameter of the root fillet 38 of thesingle-crystal turbine blade 29. In some embodiments, the referenceconical surface 70 has an apex 74 located at the nominal point 56 andhas a central axis of symmetry 72. In some embodiments, the central axisof symmetry 72 is parallel to an airfoil stacking line 40 (see FIG. 3).The reference conical surface 70 may have an inclined portion 76emanating from the apex 74 and forming an angle α with the central axisof symmetry 72. In some embodiments, angle α may be about 30°. In someembodiments, angle α may be between 25° and 35°. In some embodiments,angle α may be between 20° and 40°. In some embodiments, angle α may bebetween 10° and 80°, between 25° and 45°, between 20° and 60°, between20° and 70°, between 20° and 60° or between 30° and 45°. In someembodiments, the crystallographic orientation may be substantiallycontrolled during manufacturing so that the secondary crystallographicorientation [100] is approximately perpendicular to the reference plane64 and the primary crystallographic orientation [001] lies in thereference plane 64, orthogonal to the secondary crystallographicorientation [100]. In certain embodiments, the primary crystallographicorientation [001] may be substantially controlled to lie approximatelyon an intersection between the reference plane 64 and the referenceconical surface 70.

In these embodiments, the manufacturing process may involvessubstantially controlling the primary crystallographic orientation [001]so that it is approximately parallel to a locus of points or line formedat the intersection 80 of the reference plane 64 and reference conicalsurface 70. In some of these embodiments, the nominal point 56 may beproximal to or on the suction side 34 of the blade airfoil 30.

FIG. 9 shows stress distribution in a root fillet 38 of a single-crystalturbine blade 29 manufactured according to some aspects of the presentdisclosure. The stress distribution may be calculated using finiteelement analysis. The stress distribution shows a decrease in thestresses at the peak stress locations 68 in the root fillet 38 comparedto a blade of similar geometry shown in FIG. 7 wherein the secondarycrystallographic orientation [100] was not controlled duringmanufacturing in accordance with this disclosure.

During operation of the gas turbine engine 10, the turbine disc 35rotates at a high rotational speed when hot gases from the combustor 16impinge on the turbine blades 29, thereby imparting significantmechanical and thermal loads to the turbine blade 29 and particularlythe root fillet 38. In some embodiments, a single-crystal turbine blade29 incorporating a crystal structure manufactured according to aspectsof the present disclosure may experience comparatively lower stresses inthe root fillet 38 and thereby reduce the probability of part failure. Alower design stress in the root fillet 38 achieved by controllingcrystallographic orientation during manufacturing as described hereinmay help mitigate the need for strengthening of the single-crystalturbine blade 29 by means such as changing the root fillet shape orincreasing airfoil thickness, which may compromise the aerodynamicperformance of the airfoil 30 and/or result in additional weight.

Aspects of the present disclosure will also be applicable to turbineblades that may not be mountable to a turbine disc 35. For example,turbines blades being integral to a turbine disc 35 may also have afillet at the intersection of the blade airfoil 30 and a turbine disccircumference. Aspects of this disclosure may also be applicable toother parts of the gas turbine engine constructed from a single-crystalmaterial, such as possibly gas turbine vanes and any other machine partswherein a fillet is subjected to mechanical stresses.

The gas turbine blades and other parts discussed in the descriptionabove need not be entirely made of a single-crystal structure material.For example, only the root fillet 38 and/or airfoil 30 may be made of asingle crystal in some embodiments. For example, an airfoil portion ofsingle crystal may be provided with polycrystalline ends. In someembodiments, the platform 31, root fillet 38 and airfoil 30 may all bemade from the same single crystal.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. The present disclosure may be embodied in other specificforms without departing from the subject matter of the claims. Thepresent disclosure is intended to cover and embrace all suitable changesin technology. Modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims. Also, the scope of the claims should not belimited by the preferred embodiments set forth in the examples, butshould be given the broadest interpretation consistent with thedescription as a whole.

What is claimed is:
 1. A method of making a single-crystal turbine bladewith a material having a face centered cubic crystallographic structure,the method comprising: during manufacturing of the single-crystalturbine blade, controlling a secondary crystallographic orientation ofthe material based on a parameter of a root fillet between an airfoil ofthe single-crystal turbine blade and a platform of the single-crystalturbine blade.
 2. The method of claim 1, comprising controlling aprimary crystallographic orientation of the material to be at about 30degrees from an airfoil stacking line of the single-crystal blade. 3.The method of claim 1, comprising controlling the secondarycrystallographic orientation of the material to be substantiallyperpendicular to a reference plane that is substantially perpendicularto an edge of the root fillet.
 4. The method of claim 3, wherein thereference plane passes through a peak stress location in the rootfillet.
 5. The method of claim 4, wherein the peak stress location inthe root fillet is on a suction side of the single-crystal turbineblade.
 6. The method of claim 4, comprising controlling a primarycrystallographic orientation of the material to be substantiallyparallel to a line of intersection between the reference plane and areference conical surface, wherein: the reference conical surfaceincludes a central axis of symmetry substantially parallel to an airfoilstacking line of the single-crystal blade; and an apex of the referenceconical surface is located at the peak stress location in the rootfillet.
 7. The method of claim 6, wherein the reference conical surfaceforms an angle between 20 and 40 degrees with the central axis ofsymmetry.
 8. The method of claim 6, wherein the reference conicalsurface forms an angle of about 30 degrees with the central axis ofsymmetry.
 9. The method of claim 3, wherein the edge of the root filletis closer to the airfoil than to the platform.
 10. A turbine bladecomprising: an airfoil made of a material having a single-crystal facecentered cubic crystallographic structure; a platform connected to theairfoil; and a root fillet defined between the airfoil and the platform;wherein a secondary crystallographic orientation of the material isbased on a parameter of the root fillet.
 11. The turbine blade of claim10, wherein a primary crystallographic orientation of the material is atabout 30 degrees from a stacking line of the airfoil.
 12. The turbineblade of claim 10, wherein the secondary crystallographic orientation ofthe material is substantially perpendicular to a reference plane that issubstantially perpendicular to an edge of the root fillet.
 13. Theturbine blade of claim 12, wherein the reference plane passes through apeak stress location in the root fillet.
 14. The turbine blade of claim13, wherein the peak stress location in the root fillet is on a suctionside of the single-crystal turbine blade.
 15. The turbine blade of claim13, wherein: a primary crystallographic orientation of the material issubstantially parallel to a line of intersection between the referenceplane and a reference conical surface; the reference conical surfaceincludes a central axis of symmetry substantially parallel to a stackingline of the airfoil; and an apex of the reference conical surface islocated at the peak stress location in the root fillet.
 16. The turbineblade of claim 15, wherein the reference conical surface forms an anglebetween 20 and 40 degrees with the central axis of symmetry.
 17. Theturbine blade of claim 15, wherein the reference conical surface formsan angle of about 30 degrees with the central axis of symmetry.
 18. Theturbine blade of claim 12, wherein the edge of the root fillet is closerto the airfoil than to the platform.
 19. A method of making a turbineblade including an airfoil made of a material having a single-crystalcrystallographic structure, a platform connected to the airfoil and aroot fillet defined between the airfoil and the platform, the methodcomprising: determining a location of peak stress in the root filletexpected during use of the turbine blade; and during manufacturing ofthe turbine blade, controlling a secondary crystallographic orientationof the material based on the location of peak stress in the root fillet.20. The method of claim 19, comprising: controlling a primarycrystallographic orientation of the material to be at about 30 degreesfrom a stacking line of the airfoil; and controlling the secondarycrystallographic orientation of the material to be substantiallyperpendicular to a reference plane that is substantially perpendicularto an edge of the root fillet and that passes through the location ofpeak stress in the root fillet.